This invention relates to an operating device for an electric hoist for changing high and low speeds for raising and lowering a load by an electric hoist and more particularly controlling the speeds in a stepless manner within the high and low speed ranges.
The term "hoist" as used herein is intended to designate means inclusive a chain block having a DC motor for lifting a load.
Operating devices for electric hoists have been known disclosed such as Japanese Patent Application Laid-open No. 51-132,569. An operating device disclosed in the laid-open application comprises a switch box provided between a hook for hanging a load and a lower end of a chain depending from a main body of the hoist and push buttons for raising and lowering switches provided on a grip laterally extending from the switch box.
With such an operating device, as the push buttons are provided on the grip laterally extending from the switch box, the grip will be subjected to vertical forces when the push buttons are operated while the grip is held. Therefore, the switch box and the hook for hanging the load are often tilted so that engaging operation of the hook with the load may become difficult. In the operating device of the Laid-open application, moreover, the raising or lowering speed could not be changed. It is therefore impossible to decrease the raising or lowering speed when starting or stopping the operation in order to prevent any shock acting upon a load. It is also impossible to increase the raising or lowering speed when the load is being lifted in order to improve lifting efficiency.
An electric chain block capable of changing raising or lowering operating speed in a stepless manner has been disclosed in Japanese Utility Model Application Laid-open No. 62-189,389 filed by the applicant. With the electric chain block of the Utility Model, when changing the operating speed from high to low or low to high speed, it takes much time to arrive at low or high speed in the stepless speed control. In other words, the known chain block is inferior in responsibility in the change in speed.
The applicant has proposed a further electric chain block whose operating speed is able to be switched over stepwise from high to low or low to high speed by an alteration switch or the like and to be adjustable in a stepless manner in a high or low speed range (Japanese Utility Model Application No. 132,605/86). With this chain block, however, the change of the raising and lowering operations is carried out at an operating device provided at a location remote from a chain and a hook of the chain block. Therefore, an operator operates the electric chain block in a sense quite different from that when he is lifting a heavy object by himself. Therefore, the hitherto used electric chain blocks or hoists are lacking in simplicity in operation.